System for cold roll forming profiles having variable cross-sections

ABSTRACT

The invention relates to a system for cold roll forming profiles having variable cross-sections, with several roll stands arranged in a row, each containing a pair of rollers, between which a sheet-metal strip ( 2 ) is guided along its length (X), wherein the roll stands are moved translationally transversely to the length of the sheet-metal strip and rotationally about an axis of the roll stand during cold roll forming. According to the invention, a re-forming device ( 8, 10, 12 ) is arranged behind at least one of the roll stands and has at least one drive for generating a movement of the re-forming device in a plane transversely to the length (X) of the sheet-metal strip. On the basis of data calculated from data relating to the material and thickness of the sheet-metal strip, the configuration and control data of the roll stands and the CAD data of the profiles to be shaped, the drive is controlled in such a way that, during ongoing operation of the system, the re-forming device automatically cancels any shape deviations in the sheet-metal strip leaving the at least one roll stand.

The invention relates to a system for cold roll forming profiles having variable cross-sections according to the preambles of Claims 1 and 11. Such systems are disclosed in the German patent application DE 10 2007 059 439.0, the content of which is incorporated herein by reference, DE 100 11 755 A1, DE 2004 040 257 A1 and U.S. Pat. No. 3,051,214 A.

With such systems, profiles with cross-sections which are variable over the length are produced by not only moving the roller stands, or the adjustment stands carrying them, respectively, transversely to the longitudinal profile extension during profiling, but by also positioning the roller tools of each adjustment stand tangentially to the desired bending edge course of a profile over the entire profile length. For this purpose, the adjustment stand is enabled to perform a rotation about an axis vertical to the sheet-metal feeding plane, additionally to the possibility of adjustment transversely to the longitudinal profile extension.

It has been shown that during discontinuous roll forming of profiles with cross-sections which vary over the length, deviations from the desired shape can occur, particularly in portions where the course of the cross-section changes substantially.

If an additional shape element is present on a leg of the profile, such as the folded rim of top-hat and C-profiles, which are used as passenger car door sills or parts of the floor assembly of a vehicle and have a relatively large cross-section in relation to the metal sheet thickness, such undesired deviations in shape can be observed to an even greater extent. If the additional shape element is also vertical or nearly vertical to the forming axis, this shape element represents a stiffener and must not only be bent, but also stretched or upset (compressed), respectively.

However, even without such additional shape elements, upsetting or stretching the sheet-metal material is difficult, since the material is not deformed as desired, but at least part of the cross-section yields. The cause of such behavior is the substantial resistance of the cross-section to upsetting or stretching, respectively, and the backspringing of the metal sheet after forming. Furthermore, partially insufficient forming is also a cause of these deviations in shape.

The aim of the invention is to counteract the deviations in shape, caused by upsetting, stretching, backspringing and evasions, in a rational manner during cold roll forming of profiles with variable cross-sections.

This aim is achieved by a system of a type as set out in the characterizing features of Claims 1 and 11, respectively.

Advantageous developments of the invention are indicated in the dependent claims.

DE 10 2007 002 322 A1 discloses a method for extrusion forming from metal sheets made of light metal, where after rolling, which reduces the thickness, straightening facilitated by the process heat takes place. However, this is a continuous process where the straightening elements can be adjusted manually until the desired final cross-section is reached, and since the metal sheets are straightened in the warm state, the influence of backspringing (resilient return), which is difficult to calculate, is eliminated. In a discontinuous process, for which the invention is especially suited, numerous steps would be required to adjust the re-forming device such that the cold-rolled profile has the correct final shape.

Even if the correct final shape may possibly not be always achieved immediately with the invention, the number of adjustment steps will be reduced so as to be acceptable.

A description of embodiments by means of the figures will be found hereinbelow.

FIG. 1A shows a perspective view of a C-profile with variable width;

FIG. 1B shows a top view of the C-profile of FIG. 1A;

FIG. 1C shows five superimposed cross-sectional views of a C-profile similar to the one in FIGS. 1A and 1B along the drawn in section lines in FIG. 1B;

FIG. 2 shows an illustrative drawing of the operating method of a re-forming device;

FIG. 3 shows a perspective view of a re-forming device having three working rollers and a supporting roller;

FIG. 4 shows a schematic perspective view of a re-forming device having a small movable press; and

FIG. 5 shows a schematic diagram of a re-forming device with clamping shoes.

A known device (not shown) for cold roll forming profiles having variable cross-sections comprises a unit for cutting a sheet-metal strip in width, a driving unit for the sheet-metal strip and a forming unit.

The forming unit comprises in a known manner a series of adjustment stands, each having a roller stand containing a pair of rollers between which a sheet-metal strip is guided lengthwise. During cold roll forming, the roller stands are displaced or moved translationally transversely to the length of the sheet-metal strip and rotationally about an axis of the roller stand so as to form the sheet-metal strip to a profile having a variable cross-section. The axes of the rollers of a roller stand are frequently parallel to each other; however, the axes of rollers having diameters which are variable in longitudinal direction can also be slightly inclined with respect to each other.

The following description is made by reference to a profile with variable width, the adjustment stands being adjusted in the direction of the profile width during the passage of a metal sheet. A profile with variable width and constant height is for instance a top-hat profile or the C-profile shown in FIGS. 1A through 1C. The principles described herein, however, can also be applied to the cold roll forming of profiles with variable height and constant width or of profiles with variable width and height.

FIGS. 1A and 1B show an intermediate state in the transition to a C-profile which is supposed to a have a first portion with a constant width from A-A to B-B, a portion with constantly increasing width from B-B to D-D and a second portion with constant width from D-D to E-E. This structure is already suggested, but not yet fully developed in FIGS. 1A and 1B. From the material structure lines drawn in in FIGS. 1A and 1B, it can be seen that in portions with convex curvatures, for instance at a transition from a portion with constant width to a portion which becomes continually broader, the profile edge must be stretched. Also, in this area, a depression is frequently formed in the profile bottom (section B-B). In portions of the profile with convex curvature, for instance at a transition from a portion becoming continually broader to a portion with constant width, the strip edge must be upset (compressed), and the profile bottom frequently forms a bump (section D-D).

Thus, the discontinuities at the transitions between the various profile portions with different width along the length X of the sheet-metal strip prevent the desired forming process in the discontinuous roll forming of cross-sections. If an additional shape element is present on a lateral leg of the profile, this disadvantageous effect is even more marked. If the additional shape element is also present on a plane vertical or nearly vertical to the forming axis, such as the narrow edge sections on the top of the C--profile in FIGS. 1A through 1C, it forms a significant stiffener which must additionally be stretched or upset during forming. Even without such additional shape elements, for instance in a U-profile, upsetting or stretching the sheet-metal material is difficult since the material is not deformed as desired but the entire cross-section may yield.

To solve this problem, a re-forming unit is arranged behind at least one of the roller stands, which has at least one drive for producing a movement of the re-forming unit on a plane transverse to the length X of the sheet-metal strip, which drive is controlled, on the basis of data calculated from data concerning the material and thickness of the sheet-metal strip, the configuration and control data of the roller stands and the CAD data of the profiles to be formed, in such a way that the re-forming unit autonomously undoes any deviations in shape of the sheet-metal strip leaving the at least one roller stand due to upsetting, stretching and/or backspringing in the course of system operation.

A principle by means of which such shape deviations are eliminated is shown in FIG. 2. This figure shows a portion of a sheet-metal strip 2 between two roller stands (not shown) or in the process of leaving the last roller stand, which is again re-formed between two rollers 4 and 6. The difference between the rollers 4 and 6 of the re-forming unit of FIG. 2 and the rollers of the roller stands is that the rollers of the roller stands are normally exactly opposed to, each other on both sides of the sheet-metal strip 2, whereas the rollers 4 and 6 are mutually offset in the longitudinal direction X of the sheet-metal strip 2. By swiveling of the rollers 4 and 6 about a rotational axis which lies axially parallel between them, as shown in FIG. 1 by a bent arrow, and/or by translational displacement of the rollers, if required, deviations in shape in the sheet-metal strip 2 can be corrected.

A particularly advantageous re-forming unit is shown in FIG. 3. It works according to the three-roller method, where bending takes place around three touching lines, and contains three working rollers embodied as a forming roller 8 and two smaller rollers 10 which contact a portion of the sheet-metal strip 2 to be re-formed, and a supporting roller 12 for the two smaller rollers 10. The two small rollers 10 are advanced only for the re-forming period. Each axis of the two small rollers 10 is either advanced by a separate drive, where these drives can be supported, for instance, on the roller stand arranged before them, or the advance is performed by only one drive, where the two small rollers 10 are simply made to approach each other by reduction of the angle between the brackets 14 which retain the small rollers 10 on the circumference of the supporting roller 12. Stoppers for these movements are useful, but not mandatory.

In an alternative embodiment, the small rollers can be installed with a fixed distance, and the large roller is advanced by a suitable drive and suitable bearing.

It is also possible, with a re-forming stand having three forming rollers 8 and 10, with or without a supporting roller 12, to cause the deformation simply by rotating the re-forming stand without advancing the small rollers 10.

The rollers 4, 6 of FIG. 2 or the rollers 8, 10 and 12 of FIG. 3 can also be positioned on a separate guide and are moved by suitable drives, such as a threaded-spindle drive, servo-hydraulic cylinders or pneumatic cylinders. The guide of the rollers is advantageously mounted perpendicular to the profiling direction X. A numerical control is recommended, but point-to-point control is also possible. Fixed stops are possible as well.

If a large amount of excess or superfluous material is to be removed in the profile itself or in additional shape elements, there are two possibilities. Either the material volume is upset (compressed) into adjacent portions where it causes no disturbance and can be easily removed later on, or the material is provided with an altered geometry into which the volume has sufficient space.

In principle, stretching of the material is easier to achieve than upsetting; however, in a discontinuous roll forming process, stretching is always connected to a certain amount of upsetting in adjacent areas which is difficult to perform by the roll forming process itself, but easy to perform by means of the re-forming unit described herein.

Another solution is to introduce an additional deformation, such as a bend or a radius, in the profile contour and/or its legs. This is not a deformation in the classical sense, but rather a change in geometry which creates space for the material and yielding possibilities for the material volume. Such a deformation can be introduced in the profile, for instance, with a small co-moving press 16 such as is schematically shown on a portion of the sheet-metal strip 2 in FIG. 4. Otherwise, the existing stands can be used and the plant supplemented with small auxiliary means. It is also useful to support and hold the profile so that the re-forming can take place.

The possibilities of solution indicated here can be employed in each stage of the roll forming process. For instance, re-forming can take place at the beginning, in the middle or at the end of roll forming. Preferably, however, these operations should be performed at the end of roll forming to prevent deformed areas in the (possibly already existing) additional shape elements from being crushed during further roll forming. If necessary, some of these operations or final corrections can be performed in a downstream process outside the roll forming unit. In addition, a certain degree of deformation should already have been achieved since undesired deviations in shape increase in the course of the profiling. The following criteria are to be taken into account:

-   -   size, i. e. space occupation of the re-forming unit     -   Is the finished profile geometry an obstruction for subsequent         roll forming?     -   Alternate bending, i. e. is there too much strain on the         material due to previous intense roll forming?     -   If there is a possibility of the bend being crushed during         further deformation in the roll forming unit, re-forming should         take place at the end.

Instead of rollers, a re-forming unit can also have two guide shoes. The guide shoes are advanced at the same time as the rollers in the previously described embodiments. Here as well, driving takes place electrically, hydraulically or pneumatically. The guide shoes work like the rollers, but with sliding surface contact. Such a guide shoe unit can be installed in a fixed position before or behind a roller stand. In this case, a controlled movement transversely to the sheet-metal conveying direction or vertically to the surface of the profile cross-section segment to be deformed is necessary. Furthermore, such a guide shoe unit can also move together with the sheet-metal feed, and therefore it does not necessarily require a controlled freedom of movement along the sheet-metal feed direction. The direction of movement is advantageously parallel to the position of the strip edge in this forming stage.

Alternatively or in addition, the path curve of the sheet-metal strip can be corrected. Here, with a suitable spacing of the roller stands, a roller stand is not only moved tangentially to the predefined contour, but the path curve is traveled with an offset. This, however, is possible only with certain cross-sections, possibly with a non-deformed element (buffer element) between the individual profile segments (bottom, transition element and side wall).

Alternatively or in addition, material can be added. The cut blank is adjusted such that a certain amount of material is upset at the cross-section at the opposite bending. The additional material is accumulated at certain portions of the roller and causes a force leading to the desired bending or upsetting.

FIG. 5 shows an embodiment in which movable clamping shoes 18, 20 clamp a portion of a sheet-metal strip 2 leaving the rollers 22, 24 of a roller stand between them, thus preventing a yielding of the entire profile. The clamping shoes 18, 20 are movable or forcibly guided, respectively, in the feed direction X of the sheet-metal strip 2, possibly also inclined to it, i. e. with a component in the vertical direction Z to the plane of the sheet-metal strip. After clamping of a specific portion of the sheet-metal strip 2, the clamping shoes 18, 20 are passively entrained over a certain distance by the advance movement of the sheet-metal strip 2. The clamping is then released, and the clamping shoes 18, 20 are actively returned to their starting position.

Instead of or in addition to the clamping shoes 18, 20, supporting rollers or guide shoes can also be used. These must be positioned before and behind a roller stand. The clamping shoes, supporting rollers or guide shoes are arranged so that the profile cross-section cannot yield at the time of forming the transition between different profile sections. Holding elements for the clamping shoes, supporting rollers or guide shoes must be movable in the vertical direction Z to the sheet-metal strip plane and must be moved and controlled according to the profile contour. Such holding elements are used only at the discontinuities of the profile, i. e. at the transition points between different profile sections or in the forming of variable radii, respectively. Thus, the necessary upsetting or stretching, respectively, can be performed.

If an edge forming in the opposite direction is produced by means of a small movable press, as shown in FIG. 4, the working direction of the press is vertical to the surface of the profile with the contour to be applied. The stamp embosses the desired shape into the profile cross-section, and if necessary, adjacent profile segments are upset in the required manner. If the press operates vertically to the surface of an additional shape element, a crease can be pressed into the additional shape element so as to provide the excess material with a new geometry. In designing the press tool, it is to be ensured that only the geometry of the sheet-metal strip is changed and the sheet-metal strip is not stretched. It is recommended to use large radii in the pressing tool and to avoid clamping in the edge areas of the tool. Of course, the material is deformed, i. e. upset and stretched, in these areas as well. The aim, however, is to change the geometry.

In roll forming units with start/stop operation, a stationary press is also possible.

Another solution consists in making the inner and outer rollers of a roller stand adjustable independently of one another. Normally, the two forming rollers of a roller stand are tangentially contacting the profile contour, the connecting line of the roller centers always extending vertically to the clamped section of the sheet-metal strip. If, however, the two rollers are movable independently of one another, a controlled lateral offset of the two rollers is possible. This results in a lever, and thus a bending moment can be exercised on the profile contour, with the same operating principle as is used with the re-forming unit of FIG. 2 by means of dedicated rollers. The constructive implementation can be such that only one roller is driven and the second roller can be moved in a swiveled manner. Slewing gears with high transmission ratios, spindle drives with levers or hydraulic or pneumatic cylinders are suitable as drives for this slewing movement. The drive of the slewing movement can be controlled numerically for precise control of the deformation; however, a binary axis can also be provided since in this case, movement against a stopping point takes place and the deformation can be controlled by the movement of the entire roller stand.

Another solution consists in excising undesired portions of material already before cold roll forming, i. e. from the flat strip. Slots are introduced in portions of the sheet-metal strip which are stretched during the roll forming process, in order to facilitate deformation. In this way, the sheet-metal material itself needs only, very minor stretching in the slot areas. Notches or wedge-shaped cutouts are introduced in portions of the sheet-metal strip which have to be upset (compressed) during roll forming. Only very minor residual upsetting is then required, so as to greatly facilitate roll forming. The number, position and size of the slots and notches is selected according to the requirements. Other conditions to be taken into account are the degree of deformation, the bending radius and the material strength. Of course, the introduced slots, notches or cutouts remain within the sheet metal. This method is particularly suited if no optical or static impairments result. Otherwise, the slots, notches or cutouts can be welded and, if necessary, dressed.

Another solution consists in punctual heating of the sheet-metal strip so as to facilitate flowing of the material. If the sheet-metal strip is sufficiently heated in the points to be upset or stretched, deformation or flowing of the material, respectively, are greatly facilitated. Suitable methods are local heating with the gas-flame, laser or by induction.

Another solution consists in overbending by means of the roller stands themselves. When the profile leaves a roller stand, overbending can be achieved by additional swiveling of the roller pair, thus representing the desired contour.

The order of the deformation and re-forming steps can be of critical importance. For instance, if the folded rim of a top-hat or C-profile or the like is formed first, the profile is much stiffer in the transverse direction, thus impairing forming of the transition between different profile sections. This stiffening, however, can also have positive effects on the deformation. The decisive factor in single cases is the cross-section of the finished component. Predictions can be made on the basis of a finite element analysis. The different manufacturing strategies are to be simulated individually, compared and evaluated. 

1-12. (canceled)
 13. System for cold roll forming profiles having variable cross-sections, with several roll stands arranged in a row, each containing a pair of rollers, between which a sheet-metal strip is guided along its length, wherein the roll stands are moved translationally transversely to the length of the sheet-metal strip and rotationally about an axis of the roll stand during cold roll forming, wherein a re-forming device is arranged behind at least one of the roll stands and has at least one drive for generating a movement of the re-forming device in a plane transversely to the length of the sheet-metal strip, which drive, on the basis of data calculated from data relating to the material and thickness of the sheet-metal strip, the configuration and control data of the roll stands and the CAD data of the profiles to be shaped, is controlled in such a way that, during ongoing operation of the system, the re-forming device automatically cancels shape deviations in the sheet-metal strip leaving the at least one roll stand.
 14. System according to claim 13, wherein the re-forming device cancels shape deviations in the sheet-metal strip leaving the at least one roll stand by overbending in the opposite direction.
 15. System according to claim 13, wherein the re-forming device comprises at least two freely rotatable re-forming rollers arranged on mutually opposite sides of a portion of the sheet-metal strip, and wherein the lines along which the sheet-metal strip contacts the re-forming rollers are mutually spaced in the direction of the length of the sheet-metal strip.
 16. System according to claim 15, wherein the re-forming device comprises three freely rotatable re-forming rollers, two of which are arranged on one side of the sheet-metal strip and one of which is arranged on the opposite side of the sheet-metal strip.
 17. System according to claim 16, with one supporting roller for the two re-forming rollers arranged on the one side of the sheet-metal strip, which support themselves at an adjustable angle to each other on the circumference of the supporting roller and have a substantially smaller diameter than the re-forming roller arranged on the opposite side of the sheet-metal strip.
 18. System according to claim 13, wherein the re-forming device comprises two guiding shoes which are arranged on mutually opposite sides of a portion of the sheet-metal strip and between which the sheet-metal strip is guided substantially without play, but slidably along the length.
 19. System according to claim 13, wherein the re-forming device comprises two clamping shoes or press rams which clamp or press the sheet-metal strip between themselves and are movable and/or forcibly guided along a path extending in the longitudinal direction of the sheet-metal strip or at an inclination thereto.
 20. System according to claim 13, wherein the sheet-metal strip is partially heated by means of flames, laser beam or electromagnetic induction before it is fed into the re-forming device.
 21. System according to claim 13, wherein material is removed from, or added to, the sheet-metal strip in areas which are upset or stretched during subsequent deformation, before it is guided through the roll stands.
 22. System according to claim 13, wherein the sheet-metal strip is provided with cutouts, notches or slots in areas which are upset or stretched during subsequent deformation, before it is guided through the roll stands.
 23. System for cold roll forming profiles with variable cross-sections, having several roll stands arranged in a row, each containing a pair of rollers, between which a sheet-metal strip is guided along its length, wherein the roll stands are moved translationally transversely to the length of the sheet-metal strip and rotationally about an axis of the roll stand during cold roll forming, wherein the sheet-metal strip is provided with cutouts, notches or slots in areas which are upset or stretched during subsequent deformation, before it is guided through the roll stands.
 24. System according to claim 13, by means of which profiles with discontinuously variable cross-sections are produced.
 25. System according to claim 23, by means of which profiles with discontinuously variable cross-sections are produced. 